Volatile organic compounds including low molecular weight gases, condensable vapors, environmental tobacco smoke, bio-aerosols, among others, including, but not limited to, 1,3-butadiene, formaldehyde, acetaldehyde, benzene, toluene, acetone, methyl-ethyl ketone, hydrogen sulfide, triethylamine, pthalates, mineral oils, volatile fire retardants, etc. and irritants such as pollens or fungus spores, which are commonly referred to as organic pollutants, often constitute both a comfort concern and health hazard in an enclosed environment. Conventionally active cleaning systems such as filters, thermal catalytic beds and others, remove these organic pollutants from the environment. These systems, however, are neither energy nor cost efficient due to the pressure drop across the system or the energy required for thermal oxidation, the post conditioning of the air to acceptable temperatures, and the limited life of these systems.
Another type of cleaning system for removing organic pollutants utilizes ultra-violet (UV) to illuminate and thereby activate a photocatalytic semiconductor. In these systems the organic pollutant contacts the active surface (1), which is directly illuminated by the UV lamp (3), and is oxidized by hydroxyl radicals which have been formed thereon; "front-side" illumination. (see FIG. 1) With front-side illumination, the illumination area is limited to the "line-of-sight" of the illumination source, is inefficient due to light scattering from particulate matter between the source and the surface, and unsafe due to the potential optical hazard. An additional problem with front-side illumination can be the formation of poisonous gas, carbon monoxide, caused by the UV gas phase decomposition of some of the organic pollutants above the photocatalytic semiconductor coated substrate.
What is needed in the art is a system for safely, efficiently and effectively removing organic pollutants from a closed environment while reducing the amount of undesirable by-products.